The invention relates to a syringe comprising a piston that is slidably guided in a casing, and a needle adapted to be withdrawn into the casing.
Injection syringes for the administration of medicine or vaccine are preferably configured as one-way syringes that are to be disposed after they have been used once, and wherein a mechanism assures that they are non-usable after the first use, so as to avoid infections caused by a repeated use of the syringe. However, there is a risk that the unprotected needle of the syringe causes injuries and hence infections during or after the disposal of the syringe. In order to reduce the risk of injury, it has been common practice to mount a protective cap on the needle after the syringe has been used, so that the needle is protected in the condition in which the syringe is disposed of. Frequently, however, it is just the process of mounting the protective cap that leads to injuries.
In practice, injection syringes have become known, wherein the needle is elastically biased, so that it automatically retreats into the casing after the syringe has been used. This, however, requires a relatively complex triggering mechanism which increases the production costs of the syringes. However, disposable syringes for mass vaccinations or for the combat of endemic diseases, in particular in the third world, should be producible at low costs.